1. Field of the Invention
The present invention is directed generally to a method for point-to-multipoint connections in a self-routing ATM switching network in which signalling calls and message calls are through connected according to ATM switching principles and in which a first transmission and reception equipment and a group of further transmission and reception equipment is connected to the ATM switching network through a switching network line circuit.
2. Description of the Related Art
U.S. Pat. No. 4,491,945 discloses a method for setting up virtual connections. The virtual connections are through-connected via an ATM switching network. According to the known method, a connection between an A-subscriber and a B-subscriber is set up in a signalling cell which is transmitted through the A-subscriber to the B-subscriber before the actual data is transmitted. The signalling cell contains a cell header in which a virtual channel number is stored. The destination address for the corresponding connection is stored in the information part of the signalling cell. On the basis of the destination address, a processor which belongs to the corresponding ATM switching network determines the output of the ATM switching network to be used for the connection to be set up and also determines the virtual channel number which is valid for this output. The virtual channel number is then used in the cell header during the actual data transmission of the message cells in order to initiate the data transmission in the direction of the B-subscriber through the corresponding output of the ATM switching network.
Point-to-point connections are implemented according to the foregoing described method. Point-to-point connections are those which are set up from an A-subscriber to a B-subscriber. By contrast, point-to-multipoint are those connections which are set up from an A-subscriber to a number of B-subscribers. The above described known method can not be used for point-to-multipoint connections since the addresses of a number of destination subscribers would have to be carried along in the cell for such connections.
FIG. 1 of the present application shows a possibility for using the known point-to-point method to achieve point-to-multipoint connections. A connection is set up from a first transmission/reception means GPO to a group which consists of a number of transmission/reception means GP1, GP2 and GP3. In this case, the first transmission/reception means GPO as well as the group of transmission/reception means GP1, GP2 and GP3 represent equipment of a communication system but may also represent equipment in the sense of terminal subscribers. According to the known method, a centralized server S is involved in making the connection. In this case, a connection through the ATM switching network ASN to the centralized server S is set up from the first transmission/reception means GPO. At its output, the centralized server S duplicates the message cells and in turn forwards them to the group of transmission/reception means GP1, GP2 and GP3 through the ATM switching network ASN. Problems arise with this procedure in that the input of the ATM switching network ASN that is connected to the centralized server S is highly dynamically loaded.